1. Field of Invention
The present invention relates to a sealing method for battery containers and more particularly to fixtures by which a shape of a container formed from metal sheets can be adjusted automatically, and an original shape of the container can be restored from a deformed state, so that an entire sealing process for battery containers can be executed by automation.
2. Related Art
Because of breakthroughs in materials technology for lithium batteries, secondary batteries have become a power supplies source (e.g. lithium iron phosphate oxide) for devices which require large electricity consumption such as electric bikes and electric wheelchairs. The power storage quantity and power supply quantity of non-aqueous electrolytic secondary lithium batteries are larger than those of conventional lithium battery.
Because of breakthroughs in materials technology for lithium batteries, lithium batteries have become a power supply source (e.g. lithium iron phosphate oxide) for devices which require large electricity consumption such as electric bikes and electric wheelchairs. The power storage quantity and power supply quantity of non-aqueous electrolytic secondary lithium batteries are larger than those of conventional lithium battery. The battery container of the aforementioned secondary lithium battery is usually a metal container made of aluminum. Generally, the metal container is a container made of aluminum or stainless steel with at least one end having an opening; after an anode and a cathode, and a separator are installed in the metal container, the opening of the container is covered by a cover placing on its top, and then the opening of the container and the cover are sealed by using various sealing techniques so as to ensure a long-term and stable sealing of the battery interior to prevent moisture and air from penetrating.
Referring to FIG. 1, typically, a secondary battery 10 contains a plurality of battery cells 50 (three battery cells are shown in the drawing for an example) disposed inside a container 20 (a rectangular battery container is used as an example). Each of the battery cells 50 is composed of an anode layer, a separating layer and a cathode layer which are stacked together, and the battery cells 50 are conductively connected to electrode ends 40 disposed on a cover 30. The container 20 is made of metal sheets including one of stainless steel, nickel-plated steel, aluminum, and aluminum alloy.
Currently, for sealing of the secondary battery 10 (a rectangular battery container is used as an example), longitudinal side edges 21 and transverse side edges 22 of an opening of the container 20 are welded together with longitudinal side edges 31 and transverse side edges 32 of the cover 30 by using a welding device. Typically, a laser welding technique is used for sealing, and the technique uses an intense light source (typically a nitrogen-filled lamp) to actuate a laser resonant cavity of a yttrium iron garnet (YIG bar) to emit a single-frequency light (λ=1.06 mm), and it is focused into a beam by resonance and refraction, then the focal point is pointed at connecting portions of the longitudinal side edges 21, 31, and the transverse side edges 22, 32 of the container 20 and the cover 30 respectively, so that the corresponding edges are welded together into one body. As a result, an objective for welding and sealing of the cover 30 with the container 20 is achieved.
It should be noted that, in conventional sealing processes of the secondary battery 10, because the container 20 is made of metal sheets, thus the longitudinal side edges 21 and surfaces 23 below the longitudinal side edges 21 can be easily concavely deformed during shipping and handling; furthermore, the transverse side edges 22 and the longitudinal side edges 21 can also be easily deformed and cannot be maintained vertical to each other when a large quantity of the containers 20 are stacked on each other. Manpower has to be relied on during the sealing process of the secondary battery 10 because of the deformation problems of the container 20 mentioned above; therefore, the shapes of the containers 20 have to be adjusted manually before the battery cells 50, which are conductively connected to the electrode ends 40 of the cover 30, can be placed inside the container 20 by workers, and the connecting portions of the longitudinal side edges 21, 31, and the transverse side edges 22, 32 of the container 20 and the cover 30 have to be made flat, before proceeding with sealing by laser welding.